Hydraulic drive for industrial truck



Feb. 2, 1965 c. s. SCHROEDER HYDRAULIC DRIVE FOR INDUSTRIAL TRUCK Filed Nov. 1, 1963 INVENTOR. Cmpus S. Sch oam United States Patent Qflice Patented Feb. 2, 196 5 3,167,916 HYDRAULIQ DRIVE FGR INDUSTRIAL TRUCK Charies S. Schroeder, Villanova, Pa, assignor to Yale & Towne, 1116., New York, N.Y., a corporation of @hio Filed Nov. 1, 1963, Ser. No. 320,812 5 Claims. (Cl. 613-53) This invention relates to a hydraulic drive for an industrial truck.

In copending application Serial No. 290,552, filed June 25, 1963, by George F. Quayle, entitled Hydraulic Drive for Industrial Truck, there is shown a hydraulic drive in which fluid from a plurality of engine driven pumps is directed through a restriction to create a small back pressure for moving a spool valve. Movement of the spool valve first connects one and then additional of the pumps with a hydraulic motor, so that the mechanical advantage between the driving engine for the pumps and the hydraulic motor is decreased with resulting increase in the speed of the hydraulic motor.

Only a small flow of fluid is necessary to maintain the small pressure for holding the spool in the position connecting the pumps to the hydraulic motor, and excess flow is bypassed around the restriction and returned directly to the reservoir by the opening of a pressure relief valve. The small flow of fluid for holding the spool valve in the position connecting the pumps with the hydraulic motor is circulated through a cooler or radiator and returned to the reservoir.

While the back pressure and the flow of fluid through the restriction to create the back pressure are relatively small, they are still sufliciently large to require that an expensive radiator or cooler having a high pressure rating be used. Further, only a small portion of the total flow from the pumps flows through the cooler radiator, even when the fluid is hot and maximum cooling is desired.

The purpose of this invention is to provide an improved hydraulic circuit for a drive of this type which will permit an inexpensive radiator having a low pressure rating, such as a conventional automobile radiator, to be used for cooling the fluid, while protecting the radiator against excessive pressure and providing for increased flow of fluid through the radiator when the fluid is hot.

To this end, the restriction for creating fluid pressure for operating the spool valve is formed as a nozzle which is directed toward the radiator, and a bypass line is provided adjacent the discharge end of the nozzle and connected with the reservoir. With this arrangement, when the rate of flow and the viscosity of the fluid passing through the nozzle is such that the pressure rating of the radiator would be exceeded if all the flow through the nozzle were circulated through the radiator, the bypass line acts as a relief through which all or part of the fluid may return directly to the reservoir, thereby protecting the radiator. On the other hand, if the rate of flow and viscosity of the fluid flowing through the nozzle is such that the pressure rating of the radiator would not be exceeded, all the fluid flowing through the nozzle will be circulated through the radiator, and if this flow is not sufficient to utilize the full capacity of the radiator, the nozzle in conjunction with the bypass will act as an aspirator to draw additional fluid from the reservoir to be circulated through the radiator with the fluid passing through the nozzle.

Thus, when the fluid flowing through the nozzle is cold and thick, all or most of the fluid will be bypassed directly to the reservoir thereby protecting the radiator against excessive pressure. When the fluid becomes Warmer and thinner, all of the fluid flowing through the nozzle will be circulated through the radiator, and if the flow of fluid through the nozzle is not suflicient to feed all the fluid that the radiator will accept, additional fluid will be drawn from the reservoir and circulated through the radiator with the fluid flowing through the nozzle. Thus, maximum cooling is provided when the fluid is hot and maximum cooling therefore desired.

I have thus outlined rather broadly the more important features of my invention in order that the detailed description thereof that follows may be better understood, and in order that my contribution to the art may be better appreciated. There are, of course, additional features of my invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the con ception on which my disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of my invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of my invention, in order to prevent the appropriation of my invention by those skilled in the art.

FIG. 1 is a diagram of a hydraulic drive constructed in accordance with the invention; and

FIG. 2'is an enlarged sectional view of the nozzle and mechanism for adjusting the position of the discharge end of the nozzle relatively to the bypass conduit.

Referring to the drawings, and in particular to the diagram of FIG. 1, the present invention is shown applied to a hydraulic drive of the type described in application Serial No. 290,552, previously referred to.

The drive includes three pumps 10, 11 and 12, which are adapted to be simultaneously driven by an engine 13; a pair of hydraulic drive motors 14 and 15,'which are adapted to be driven by fluid under pressure supplied by the pumps 10, 11 and 12; and a fluid pressure operable speed control valve 16 adapted to first connect pump 10,

then pump 11, and finally all three pumps 10, 11 and 12 to the hydraulic motors 14 and 15 to decrease the mechanical advantages between the engine 13 and the hydraulic motors 14 and 15 and therefore increase the speed of the hydraulic motors.

The three pumps 10, 11 and 12 are connected to a reservoir 17 by an intake line 18 and each pump is connected by separate discharge lines 19, 20 and 21, respectively, to valve 16. The hydraulic motors 14 and 15 are connected to the speed control valve 16 by lines 22 and 23.

The speed control valve 16 and its operation modescribed in detail in said application Serial No. 290,552,

in excess of that necessary to create the back pressure to operate the valve 16 is bypassed through the line 25 to the reservoir '17 by the opening of a pressure relief valve 26.

In accordance with the invention, the restriction in line 247is formed as a nozzle 26 which is connected with a line 27 to the intake opening 28 of a radiator or cooler 29, and a bypass line 39 provided adjacent the discharge end 25a of the nozzle 26 which connects the line 27 with the reservoir 17.

With this arrangement, when the fluid flowing through the nozzle 26 is cold and thick, all or most of the fluid will be bypassed directly to the reservoir 17 through the bypass line 30, therefore protecting the radiator 29 against excessive pressure. When the fluid becomes warmer and thinner all of the fluid flowing through the nozzle 26 will be circulated through the radiator 29 and back to the reservoir 17 through a line 31. If the fluid flowing through the nozzle 26 is not suflicient to feed all the fluid that the radiator 29 will accept, additional fluid Will be drawn from'the reservoir 17 by aspirator action between the nozzle 26 and the bypass line 39, and will be circulated through the radiator 29 with the fluid flowing through the nozzle 26. Thus, maximum cooling is provided when the fluid is hot and maximum cooling desired.

The maximum pressure exerted on the radiator 29 by the fluid is determined by the position of the discharge end 26a of the nozzle 26 relatively to the bypass line 30. Thus, by adjusting the position of the discharge end 26a relatively to the bypass line 30, it is possible to limit the maximum pressure exerted on the radiator to allow a very inexpensive radiator having a low pressure rating, such as for example a conventional automobile radiator, to be used, while ensuring that the full capacity of the radiator is utilized when the fluid is hot.

In the form of the invention disclosed in the drawings, the discharge end 26a of the nozzle 26 is slidably received in an opening 32 which is provided in a fitting 27a on the end of the line 27 and a suitable seal 13 provided to prevent leakage between the nozzle 26 and the fitting end of the fitting 27a and extend through openings in a flange 35 formed on the nozzle 26; The studs 34- are A pair of threaded studs 34 are securedto the,

provided with a pair of nuts 36 and 37, positioned one on each side of the flange 35. The position of the discharge end 26a of the nozzle 26 may be quickly and easily adjusted relatively to the end of the bypass line 3010 adjust the pressure in accordance With the pressure rating of the radiator by turningthe nuts 36 and 37 to slide the nozzle 26 inwardly or outwardly of the end of the fitting fications may be made'therein without departing from the spirit and scope of the invention.

I claim:

1. In a hydraulic circuit, a fluid reservoir, a radiator, passage means connected to said radiator through which fluid'may pass into said radiator, a fluid conducting passagev for fluid to .be cooled by said radiator terminating in a pressure nozzle in said passage means, bypass conduit means connected at one end to said passage means adjacent the discharge end of said nozzle and connected at the opposite end to said reservoir.

2. In a'hydraulic drive, a fluid reservoir, 'a radiator,

passage means connected to said radiator through which fluid may pass into said radiator, a fluid conducting p assage for fluid to be cooled bysaid radiator terminating in a pressure nozzle in said passage means, bypass conduit means connected at one end .to said passage means adjacent the discharge end of saidtnozzle and connected at the opposite endlto said reseiyoir whereby fluid may be bypassed to saidreservoir as it flows out of said nozzle, or be drawn from said reservoir through said bypass adjacent the discharge end of aid nozzle and connected at the opposite end to said reservoir whereby fluid may be bypassed to said reservoir as it flows out of said nozzle or be drawn from said reservoir through said bypass and into said radiator by aspirator action ofsaid nozzle whereby to provide full utilization of the capacity of said radiator dependingon the flow characteristics of said fluid without exceeding the pressure rating of said radiator, and means for adjusting the position of said discharge end of said nozzle relatively. to said one of said bypass conduit means.

4. A hydraulic drive having a reservoir, a plurality of pumps, a hydraulic motor, a valve operable by fluid pressure to connect said pumps to said hydraulic motor, a radiator having a relatively low pressure rating, passage means through which fluid may flow from said pump and hydraulic motor to said radiator for cooling, restricting means in said passage means for creating back pressure for operating said valve, pressure relief valve means for bypassing fluid around said restriction and radiator when the. flow of fluid is in excess of that necessary to create said pressure for operating said valve, said restriction means being in the form of a nozzle with the discharge end'of said nozzle directed toward said radiator, and bypass conduit means conuected at one end to said passage means adjacent the discharge end of said nozzle and connected at the opposite end to said reservoir whereby fluid may be bypassedto or drawn from said reservoir by aspirator action between said nozzle and bypass passage means as necessary to provide full utilization of the capacity of said radiator without exceeding the pressuring rating of said radiator.

5. A hydraulic drive having a reservoir, a plurality of pumps, a hydraulic motor, a valve operable by fluid pressure to connect said pumps to said hydraulic motor, a radiator having a relatively low pressure rating, passage means through which fluid may flow from said pump and hydraulic motor to said radiator for cooling, restricting means in said passage means for creating back pressure for operating said valve, pressure relief valve means for bypassing fluid around said restriction and radiator when the flow of fluid is in excess of that necessary to create said pressure for operating said valve, said restriction means being in the form of a nozzle with the discharge end of said nozzle directed toward said radiator, bypass conduit means connected at one end tosaid passage means adjacent the discharge. end of said nozzle and connected at the opposite end to said reservoir whereby fluid may be bypassed to or drawn from said reservoir by aspirator action between said nozzle. and bypass passage means as necessary to provide full utilization of the capacity of said radiator without exceeding the pressuring rating of said radiator, and'means for adjusting the position of said discharge end of said nozzle relatively to said bypass conduit means. t

No references cited. 

1. IN A HYDRAULIC CIRCUIT, A FLUID RESERVOIR, A RADIATOR, PASSAGE MEANS CONNECTED TO SAID RADIATOR THROUGH WHICH FLUID MAY PASS INTO SAID RADIATOR, A FLUID CONDUCTING PASSAGE FOR FLUID TO BE COOLED BY SAID RADIATOR TERMINATING IN A PRESSURE NOZZLE IN SAID PASSAGE MEANS, BYPASS CONDUIT MEANS CONNECTED AT ONE END TO SAID PASSAGE MEANS ADJACENT THE DISCHARGE END OF SAID NOZZLE AND CONNECTED AT THE OPPOSITE END TO SAID RESERVOIR. 